La2-xSrxCaCu2O6 samples were prepared at 1050°C under 20 atm oxygen pressure. By various kinds of measurements, it was found that their superconducting volume fractions were very small due to the presence of weak electron localization caused by oxygen deficiency. Then, the electronic specific heat coefficient γ could be determined from the specific heat data measured at low temperature, considering that weak localization does not significantly affect the γ values. The results show that as the hole carrier density of the high-Tc Cu oxide system decreases or the system approaches the metal-insulator boundary from the metallic side, γ decreases in contrast to the cases of other Mott-Hubbard systems.
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